14.127 Behavioral Economics. Lecture 12 Xavier Gabaix April 29, 2004 0.1 Twin stocks • Shell and Royal Dutch–claims on the same company • There is a difference between prices • The difference is driven by the difference in aggrogate movements in London vs Dutch stock markets • Sharpe ratio (expected return/standard deviation) of this aribtrage is not great 0.2 Are noise traders eliminated from the market? • Might be both positive and negative • If γ is large enough, then E (RNT − RA) > 0 and noise traders prevail • This is because noise traders are more optimistic and take more risk • But by construction EUA > EUNT • Stock returns look like a random walk [see slides] • Evidence from stock splits – supports efficient market hypothesis [see slides] • Event study methodology [see slides] • Jensen: “The Efficient Market Hypothesis is the best established fact in all of social sciences” • de Bondt and Thaler JoF 1985 [see slides] • Value vs growth [see slides]: a recent attempt at explanation by consumption covariance – growth stocks have low covariance with consumption because most of risk is idiosyncratic; conversely GM has high covariance (Parker, Julliard, Barsal) • Initial Public Offerings [see slides] 0.3 Campbell-Cochrane “By force of habit” JPE 1999 • Explains low equity premium in booms and high in recessions where Xt is your habit surplus/consumption ratio, st = ln St < 0. • “Catching up with the Joneses economy” – what makes me happy is not my consumption compared to my past consumption (internal habit) but my consumption compared to past consumption in the economy (external habit). • This is too simplify the problem: noone’s current consumption impacts his or her future habit • Representative consumer economy. Aggregate • Postulates where g is mean growth rate and φ ∈ (0, 1) determines mean reversion. • Lucas economy • Euler equation with • They postulate 1 +r = E [Mt+1] is constant • Hence • To price stocks, use to write the Euler equation as • Thus • Postulate, and solve for f (st).